Post-traumatic stress disorder (PTSD) is a psychiatric condition with severe symptoms associated with biological dysregulation that can occur after exposure to shock. Exposure to trauma results in modulation in the hypothalamic-pituitary-adrenal (HPA) axis, which plays a critical role in the stress response that in turn interacts reciprocally with the immune system to maintain homeostasis. To date, over 1.6 million US men and women have served in the wars in Iraq (Operation Iraqi Freedom, OIF) and Afghanistan and surrounding regions (Operation Enduring Freedom, OEF). Over 35% of returned Iraq and Afghanistan veterans in Department of Veterans Affairs (VA) care have received mental health diagnoses, the most prevalent being PTSD. Inasmuch as, there is significant prevalence of PTSD in combat veterans who have served in the Iraq and Afghanistan wars, our studies have focused on addressing the pathological basis of immune dysfunction in these men and women. In the current study, we will test the central hypothesis that PTSD associates, at least in part, with dysregulation in the epigenetic mechanisms that control the differentiation of Th1/Th2/Th17/Treg cells of the adaptive immune response, thereby altering the cytokine profiles and promoting inflammatory response. The specific aims are 1) to corroborate the serum cytokine profile with severity of PTSD and to determine the role of transcription factors that regulate the differentiation of Th/T reg cells. Furthermore, whether the cytokine expression in Th/Tregs is dependent on the mitogen activated protein kinase signaling pathway will be elucidated. 2) to address whether epigenetic mechanisms play a role in Th/Treg polarization by performing high-throughput microRNAs arrays and to determine the level of hypo- or hypermethylation of Th1, Th2, Th17 and Treg cytokine/transcription factor gene promoters. The miRNA data generated will be used in silico algorithms for related target gene prediction and pathways that are dysregulated. Further studies will be performed to assess whether reversal of the cytokine expression occurs in the T cells following transfection with miRNA mimics or antagomirs of miRNAs that are downregulated or upregulated respectively. Based on the methylation data, demethylation will be attempted using inhibitors for hypermethylated gene promoters of cytokines or their transcription factors to determine whether this would lead to reversal of the Th/Treg phenotypic characteristics. Together, these studies are novel in that they will not only help understand stress-induced alterations in immune profiles in PTSD patients but will also provide useful clues on whether epigenetic markers and specific cytokines/chemokines can serve as bio-markers of PTSD.